1. Field of the Invention
This invention relates to a laser diode (hereinafter referred to as "LD") module and, more particularly, to an LD module capable of improving optical coupling efficiency between an LD chip and an optical fiber without reducing life span reliablity on a CAN-packaged LD chip.
2. Description of Related Art
LD module is a module for optical telecommunication in which an LD light source incorporating an LD chip is optically coupled to an optical fiber. As the LD light source, an LD light source having a structure, as a CAN package, that an LD chip is mounted with an LD preservation gas having a main component of an inert gas has been known to improve the life span reliability.
With such an LD module, LD light emitted from the LD chip is polarized in a prescribed direction, and is radiated in an elliptical shape to one end of the optical fiber. The optical coupling efficiency between the LD light source and the optical fiber is therefore generally low, and to compensate this, the LD chip has to be used with a large output. When the LD chip is used with a large output, however, the life span of the LD chip is shortened as a current status, thereby raising a problem of low life span reliablity in the LD module.
As a means for improving the optical coupling efficiency of the LD module without using the LD chip with a large output, forming a convex fiber lens on one end of the optical fiber for effectively condensing the LD light by correcting an aspect ratio of the LD light has been proposed (see, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-86,923 or Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-5,865). With an LD module of this kind, the LD chip can be used with a lower output, so that the chip can keep the life span reliability.
A following problem, however, may occur where an optical fiber having a convex fiber lens is coupled to an LD light source having a CAN package structure. That is, because the convex fiber lens has a very short focal distance, the lens must be ordinarily placed in proximity of 1 to 20 microns from the LD chip. Accordingly, the one end of the optical fiber, together with the convex fiber lens, must be inserted in the above CAN package. However, it is very difficult with the current technical level to maintain an adequately gas-sealed state where the one end of the optical fiber is inserted in the above structure.
This invention is devised in consideration of the above problems. It is an object of the invention to provide an LD module capable of improving optical coupling efficiency between an LD chip and an optical fiber without reducing life span reliability on a CAN-packaged LD chip. Other objects of the invention can be understood from the description of this specification as below.